1. Field of the Invention
The present application relates to optical device components and more particularly to connecting optical device components having mismatched coefficients of thermal expansion (CTEs).
2. Brief Description of Related Art
Although there is a desire for many optical and structural components used in military and aerospace applications to be made out of one common optical material, such as silicon carbide, it is often impractical to design an entire optical device assembly out of such materials. Silicon carbide and similar optical materials provide a favorably low coefficient of thermal expansion (CTE) but are brittle and typically may not satisfy the structural capabilities required by a support structure.
For this reason, typically, an interface system between the silicon carbide structure and the remainder of the assembly is used, which most often is made from a higher CTE metallic material, such as aluminum or steel. Because of the significant mismatch in CTE between optical materials, such as silicon carbide and metallic material, large stresses can develop when such assembly is subjected to a temperature change. Due to the brittle nature of optical materials, the thermally induced stresses can cause fracture in the optical materials and metals unless the interface system is provided to mitigate the induced stress.
Several existing techniques are used to attach materials with dissimilar CTEs that will be subjected to conditions spanning a range of temperatures:
One existing technique uses “soft” attachments, made out of a flexible material, between the two CTE mismatched components to accommodate differential expansion/contraction. However, the movement permitted by flexible mounts is often unacceptable because telescopes and their support structures commonly need to be held rigidly together to maintain accuracy and alignment. Therefore, this method may work for relatively small components where thermal expansion is minimal, but may not be effective for any larger optical device components.
Another existing technique uses flexures, which are designed to flex and eliminate stresses induced by thermal effects. However, depending on the materials, they may or may not be effective. For example, brittle materials cannot use flexures due to increased risks of material fracture.
Other existing techniques use complex metering structures to mitigate the thermal effects. However, these metering structures add several complicated components to the assembly, resulting in substantial and undesirable increases in weight, complexity, and cost of the products.